commit a87fc5e9e033fdc02713d15cd2d2afdfecd20ddc
author Mark Seaborn <mseaborn@google.com> Tue Feb 28 00:11:19 2023 +0000
committer CQ Bot <fuchsia-internal-scoped@luci-project-accounts.iam.gserviceaccount.com> Tue Feb 28 00:11:19 2023 +0000
tree 07afd74728db93e3dd020c668cb60036e430d3c0
parent 6c1fd41cbed2750288848c0b5e3b90f16d6e3374

[kernel][ktrace] Fix race condition in ktrace record creation (reland #2)

This change fixes a bug in ktrace that could manifest as a failed
debug assert.  See https://fxbug.dev/120711 for details.

Remove unused PendingCommit::observed_grpmask_ field.

Replace grpmask_and_inflight_writes_ with a new field, write_state_
that encodes both the in-flight count and a writes-enabled bit.
Because we emit group-less name records at trace initialization, group
mask alone is insufficient to control whether writes are enabled.

Move the group mask into its own dedicated atomic field that's checked
by writers before attempting to increment.

Change KTraceState::IncPendingWrite to only increment if writes are
enabled and return false otherwise.  KTraceState::Reserve will now
fail with ZX_ERR_BAD_STATE if called when tracing is stopped.

This is a reland.  The earlier two versions were:

 * https://fuchsia-review.googlesource.com/c/fuchsia/+/801688

   The change from that version is to fix an assertion in
   DecPendingWrite() (and to add a test for that).

 * https://fuchsia-review.googlesource.com/c/fuchsia/+/804268

   The change from that version is to do IncPendingWrite() before
   ReserveRaw() so that we don't create trace records with zero
   headers when writing to the trace buffer has been disabled (and to
   add a test for that).

Those original versions were authored by Nick Maniscalco.

Bug: 120711
Bug: 122181
Change-Id: Iab89c17e06a3987e83e4fac4c0d425a4085cdf8b
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/810689
Commit-Queue: Mark Seaborn <mseaborn@google.com>
Reviewed-by: John Grossman <johngro@google.com>